Mauro,
This pistol definitely looks like a custom made long barrel .22 caliber target pistol based on one of the post war .22 caliber Luger conversion kits...with a fixed barrel instead of the insert type barrel. Naturally custom sights were added to the conversion rear toggle.
But of most interest to me is the pistol on the bottom of the photo.
Are more photos of this other pistol available?
This Francotte Training pistol was designed as a single shot training pistol... only 200 were produced by Messrs. Auguste Francotte, Belgium . The pistol you show is in VERY nice condition. The Hermann-Historica auction website sold one of these a couple of years ago and it sold for 6136 Euros.
Here is a link to a message thread where this type of pistol was discussed.
http://forums.lugerforum.com/cgi-bin/lugerforum/ultimatebb.cgi?ubb=get_topic;f=9;t=00 0049